1. Field of the Invention
The subject of the present invention is an electrohydraulic device for closed-loop control of the control jack of a variable compression ratio engine comprising at least one hydraulic transfer valve and one control rack position sensor.
2. Description of the Related Art
According to international patents WO98/51911, WO00/31377 and WO03/008783 belonging to the applicant, various mechanical devices for a variable displacement engine are known.
It is noted that international patent WO98/51911 in the name of the applicant describes a device used to enhance the overall efficiency of internal combustion engines with pistons used at variable load and speed by in-operation adaptation of their effective displacement and/or of their volumetric ratio. Since this type of engine is known to those skilled in the art by the name “variable compression ratio engine”, this name will be adopted in the following text.
It is noted that, according to international patent WO00/31377 in the name of the applicant, the mechanical transmission device for a variable compression ratio engine comprises a piston that is secured in its bottom portion to a transmission member interacting on the one hand with a rolling guidance device and, on the other hand, with a gearwheel secured to a connecting rod making it possible to transmit the movement between said piston and said connecting rod.
It is noted that, according to international patent WO03/008783 in the name of the applicant, the mechanical transmission device for a variable compression ratio engine comprises at least one cylinder in which a piston moves which is secured, in its lower portion, to a transmission member interacting on the one hand via a small-dimension rack with a rolling guidance device and, on the other hand, by means of another large-dimension rack, with a gearwheel secured to a connecting rod.
Said mechanical transmission device for a variable compression ratio engine also comprises at least one control rack interacting with the gearwheel, means for attaching the piston to the transmission member which offer a clamping prestress, connection means which make it possible to stiffen the teeth of the racks, and means for reinforcing and lightening the structure of the gearwheel.
It is observed that according to international patents WO98/51911 and PCT/FR2007/000149, the compression ratio of the variable compression ratio engine is regulated by means of a control hydraulic jack the movement of which is provided by the forces resulting from the inertia of the moving parts and from the pressure of the engine gases which are applied to the control rack to which said jack is secured. According to these patents, it is noted that the position of the control jack always follows that of a control rod which acts on the opening or closing of valves which are in contact with the top and bottom faces of the piston of the control jack. Said valves allow the hydraulic fluid to pass from the top chamber to the bottom chamber of the control jack or vice versa either to decrease or increase the compression ratio of the variable compression ratio engine. Patents PCT/FR2007/000150 and PCT/FR2007/000147 describe a number of variants making it possible to regulate the position of the control rod by means of one or more electric motors controlled by at least one computer.
It is also noted that, according to patent PCT/FR2007/000149, the control jack comprises a pressurized hydraulic fluid inlet provided to compensate for any leaks from said control jack, and to provide a preload pressure for the purpose of increasing the accuracy of retention of the setpoint in the vertical position of said control jack by reducing the effects of the compressibility of the oil while preventing any cavitation phenomenon.
As claimed in international patent application PCT/FR2007/000147 in the name of the applicant, a single electric motor can control the compression ratio of several cylinders via a cam or eccentric shaft. In this same patent, it is seen that the regulation of the initial compression ratio of each cylinder may be carried out by means of an independent regulation device that can be a threading immobilized in rotation.